Fuel cell systems such as residential cogeneration systems include a hydrogen generating apparatus configured to generate a hydrogen-containing fuel gas, and fuel cells configured to generate power by utilizing the fuel gas generated by the hydrogen generating apparatus.
A hydrogen generating apparatus for a fuel cell system includes: an evaporator for mixing a source gas such as hydrocarbon-based fuel (e.g., town gas, LPG) with water vapor; a reformer for allowing steam-reforming reaction of the mixture gas to occur at a high temperature of around 600° C. to 800° C. to generate a hydrogen-containing gas containing hydrogen as primary component; a shift converter for reducing the level of carbon monoxide, a substance which is poisonous to catalyst used in the fuel cells, to around 0.5% by the CO shift reaction; and a CO remover for further reducing the carbon monoxide level to around 10 ppm by a selective oxidation reaction (see, e.g., Patent Literature 1).
A cross-section of a hydrogen generating apparatus that has already been proposed (see Patent Literature 1) is illustrated in FIG. 10. Hydrogen generating apparatus 1 illustrated in FIG. 10 includes evaporator 10, reformer 2, shift converter 3, CO remover 4, and combustor 6.
Evaporator 10 includes inner cylinder 11, outer cylinder 12, and spiral evaporation channel 18 defined by a spiral coil of round rod (channel defining member) 50 provided between inner cylinder 11 and outer cylinder 12. Further, inner cylinder 11 and outer cylinder 12 can each be fabricated by, for example, vertically welding a rolled stainless steel plate.
Such evaporator 10 is fabricated by, for example, inserting inner cylinder 11 into outer cylinder 12 in which a spiral coil of round rod 50 is welded to the inner circumference surface thereof, and expanding inserted inner cylinder 11. By expanding inner cylinder 11 inserted into outer cylinder 12, the outer circumference surface of inner cylinder 11 and round rod 50 come into contact with each other and thereby spiral evaporation channel 18 is formed between inner cylinder 11 and outer cylinder 12.
To spiral evaporation channel 18 of evaporator 10 having such a configuration are supplied a source gas and water to be reformed. The source gas is supplied from source feeder 15; and the water is supplied from water feeder 16. The water supplied to evaporation channel 18 is evaporated by being heated by combustion gas flowing through combustion gas channel 14. As a result, in evaporator 10, a mixture gas of the source gas and water vapor is produced.
Further, by providing evaporation channel 18 in the form of spiral, it is possible to increase the length of evaporation channel 18, thereby making it possible to increase the amount of heat supplied to water to be reformed 17 while water passes through evaporation channel 18. As a result, it is possible to facilitate evaporation of water to be reformed 17. This makes it possible to increase the amount of water vapor used for steam reforming reaction in the reformer.
Further, a method is proposed in which the evaporation channel is defined by, instead of the rod wound in spiral form, a protrusion formed on the inner circumference surface of the outer cylinder or the outer circumference surface of the inner cylinder (see Patent Literature 1 or 2).
Further, a technique is known that uses a metal tube that is spirally wound around the outer circumference surface of the inner cylinder as a evaporation channel (see, for example, patent literature 3). In the hydrogen generating apparatus disclosed by Patent Literature 3, a source gas and water to be reformed flow in a metal tube that is wound around the outer circumference surface of the inner cylinder in the form of spiral.